Azure Function App日志级别配置失效：低Severity日志仍输出

你的问题核心是Serilog日志级别过滤未生效，低级别日志仍被输出。结合你的代码与Azure Functions运行特性，从以下几个方向修复：

1. 调整Serilog配置顺序，确保全局级别优先生效 #

Serilog的MinimumLevel是全局过滤规则，需在添加任何输出目标（Console、ApplicationInsights）前设置，否则可能被输出目标的默认配置覆盖。修改代码顺序如下：

public static void ConfigureLogging(IServiceCollection services)
{
    var loggerConfiguration = new LoggerConfiguration()
        .Enrich.FromLogContext();

    string applicationInsightsInstrumentationKey = Environment.GetEnvironmentVariable("APPINSIGHTS_INSTRUMENTATIONKEY");
    if (!string.IsNullOrEmpty(applicationInsightsInstrumentationKey))
    {
        // 先处理日志级别配置
        var environmentEnv = Environment.GetEnvironmentVariable("Environment")?.ToLower();
        if (!string.IsNullOrEmpty(environmentEnv))
        {
            var environmentLogLevel = (int)Enum.Parse(typeof(LogLevels), environmentEnv, ignoreCase: true);
            switch (environmentLogLevel)
            {
                case 1:
                    loggerConfiguration.MinimumLevel.Debug();
                    break;
                case 2:
                    loggerConfiguration.MinimumLevel.Information();
                    break;
                case 3:
                    loggerConfiguration.MinimumLevel.Warning();
                    break;
                case 4:
                    loggerConfiguration.MinimumLevel.Error();
                    break;
                default:
                    loggerConfiguration.MinimumLevel.Error();
                    break;
            }
        }
        else
        {
            // 环境变量未设置时默认Error级别
            loggerConfiguration.MinimumLevel.Error();
        }

        // 再添加输出目标
        var outputTemplateString = "[{Timestamp:HH:mm:ss} {CorrelationId} {Level:u3}] {Message:lj} ({SourceContext}){NewLine}{Exception}";
        loggerConfiguration.WriteTo.Console(outputTemplate: outputTemplateString);

        var telemetryConfiguration = TelemetryConfiguration.CreateDefault();
        telemetryConfiguration.InstrumentationKey = applicationInsightsInstrumentationKey;
        loggerConfiguration.WriteTo.ApplicationInsights(telemetryConfiguration, TelemetryConverter.Traces);
    }

    Log.Logger = loggerConfiguration.CreateLogger();
    services.AddSingleton(Log.Logger); // 修复语法错误：添加分号

    // Azure Functions中使用Worker Service版本的Application Insights配置
    services.AddApplicationInsightsTelemetryWorkerService();
}

2. 修正Azure Functions宿主日志配置 #

Azure Functions的host.json会覆盖部分日志过滤规则，即使Serilog配置了Error级别，宿主仍可能输出低级别日志。在项目根目录创建/修改host.json：

{
  "logging": {
    "logLevel": {
      "Default": "Error",
      "Microsoft": "Error",
      "Microsoft.Hosting.Lifetime": "Error"
    },
    "applicationInsights": {
      "samplingSettings": {
        "isEnabled": true,
        "excludedTypes": "Request"
      }
    }
  }
}

3. 验证环境变量与枚举的正确性 #

• 确保Environment环境变量的值与你的LogLevels枚举定义匹配（代码已添加ignoreCase: true避免大小写问题）
• 确认枚举定义示例：

  public enum LogLevels
  {
      Debug = 1,
      Information = 2,
      Warning = 3,
      Error = 4
  }
  

4. 排查编译与运行时错误 #

• 修复代码中services.AddSingleton(Log.Logger)后的缺失分号，避免编译失败
• 确认APPINSIGHTS_INSTRUMENTATIONKEY已正确配置在Azure Function App的应用设置中

内容的提问来源于stack exchange，提问作者Warfujjii